Type of Document	Dissertation
Author	Drum, Matthew John
Author's Email Address	matthew.drum@famu.edu
URN	etd-04072006-190210
Title	Expression of Axdazl and Axvh in Axolotl Germ Cells, Suggest that Regulative Germ Cell Specification is a Primitive Trait Conserved in the Mammalian Lineage.
Degree	Doctor of Philosophy
Department	Biological Science, Department of
Advisory Committee	Advisor Name Title Henry W. Bass Committee Chair Cathy W. Levenson Committee Member George W. Bates Committee Member Gregory M. Erickson Committee Member Robert H. Reeves Committee Member
Keywords	Axdazl Chocolate Lungfish Urodele Development Germ cell PGC Axolotl Axvh
Date of Defense	2006-04-06
Availability	unrestricted
Abstract How germ cells are specified in animal embryos has been a mystery for decades. Unlike most developmental processes, which are highly conserved, embryos specify germ cells in very different ways. The embryos of several prominent model organisms contain germ cell determinants (germ plasm) that segregate to germ cell precursors. In other animals, including mice, germ cells form in response to regulative mechanisms during development. It has been suggested that the germ line is specified similarly in urodele amphibians. To investigate the similarity between urodeles and mice, I cloned two genes from the salamander Ambystoma mexicanum (axolotl) that are required for proper germ cell formation in all organisms examined to date. During development, the orthologs of vasa and daz-like genes are maternally inherited in the animal cap and equatorial regions of the oocyte and are up-regulated in PGCs of tail bud embryos before the gonad forms. Axvh and Axdazl RNA display no cytoplasmic localization in gonadal PGC’s, but are expressed ubiquitously throughout the female germ cell cycle. Similarly, in mouse embryos germ cells are specified by extracellular signals; they are not autonomously specified by maternal germ cell determinants (germ plasm) and I can confirm previous experiments proposing the germ cells in axolotls arise from naive mesoderm in response to simple mesoderm inducing agents (in a mechanism similar to mice). Finally, using phylogenetic and comparative analysis, I demonstrate urodele amphibians share a common mechanism of germ cell development that is ancestral to tetrapods, and retained in the mammalian lineage and that germ plasm, as found in species such as frogs and teleosts, is the result of convergent evolution; furthering the development of the axolotl as a viable experimental system for studying germ cell formation in mammals.
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